$149 Monoprice Tube Hybrid Amp

Not sure about Monoprice' policies, but refurbs often go through more extensive testing than new production. I've bought refurb many times with excellent results, never sent anything back. Many are just returns due to damaged shipping cartons, torn or crunched corners, but they are absolutely fine with no playing time. I used to work in receiving at an electronics firm and people refuse shipments for many reasons without even opening them, but once shipped out and back the policy was to open it and it got a thorough retest, shake, retest, rebox, sold as refurb. Often returns are just from customer confusion as to setup.

 

Question for the Monoprice Hybrid Tube Amp owners out there.

Bought one on sale last week, received it yesterday, hooked it up last night.

Great sound! Love it! I wanted to stay up all night listening to the thing, but, alas, sleep caught up with me. Oh, and for 25 W per channel, it really seemed to put out the sound.

Here's the question, my wife noticed this. The 2 outer tubes light fully light up, the inner ones it seemed just their tips lit up. Is this normal?

Thanks,

Charlie

 

Yes, the outer pair light up like a new saloon. The inner pair are more subdued--the structure hides the filaments more. The Russian military tubes I bought to roll in mine are exactly the same.

 

Nah...

 

Thanks a bunch, BuddhaBob. Kinda figured as good as it sounded, there really couldn't be anything wrong. Still, nice to know everything is truly in working order. Man, folks, for the price paid, such a bargain for the body and detail it puts into the sound. I never really gave much thought to the role of amps, I believed much more in good speakers, and the "playback equipment" for want of a better term. I'm convinced.

 

If this was a dedicated headphone amp - yes, maybe. But, the headphone tap on this unit is almost definitely connected to a padded down offshoot of the power section, which will give you, uhm, maybe 1W of power and no sound to brag about.

I have a top of the line Cambridge Audio Azur 851A integrated, which set me back $1,850.00. I was not too happy with the sound coming from its headphone jack, and wound up buying a dedicated phones amp.

This $150 integrated cannot give you any better headphone sound, unless you can somehow tweak it to give its full output (30W) to the headphone jack. But that may be dangerous to your health.

 

The MP amp plays better with some headphones than others. Higher impedance helps, over 40 ohms at least. It isn't amazing in that department, but some users have had very good results. The best headphone jack I have to plug into is on my DAC, an Emotiva Stealth DC-1. My vintage Yamaha C80 preamp is next, then the MP amp, as far as quality and oomph. But I only listen to phones an hour or two a month, pretty rare. Maybe even less this summer since I am enjoying the MP sound via speakers, often for hours daily. The sound is far from perfect, but very engaging. It's odd, as I have various very nice SS and tube amps to choose from, but they have made a hybrid that is simply mellifluous and almost dirt cheap.

Adjusted for inflation since 1970 when I started buying serious gear, this U$150 amp would have been about U$24 then. Still amazing to me.

 

Very well, sir. I'll take your point. After all - you have heard it, and I have not. Just figured that a $150 amp cannot sound better than my $2k amp. Perhaps it can, after all.

 

Not at all. I would be very surprised if that were the case. I only marvel that it sounds much better than it should.

 

Just a first look inside this morning. They use 4558 Op Amps, one for each channel, on the headphone out and it isn't tapping off the tube or final output. I haven't traced it out fully, but my MP innards look pretty much identical to the pictures early on in this thread.. The outputs are individual LM1875s on substantial heat sinks. It hardly gets warm at high volume. My MP innards look pretty much identical to the pictures early on in this thread.

Not padded down but nothing to brag about, as you said, just "not bad" I suppose.

Headphone drivers: http://www.ti.com/lit/ds/symlink/rc4558.pdf
Final SS: http://www.ti.com/lit/ds/symlink/lm1875.pdf

 

I am tempted to pull the metal tube rings now that I am inside. Buck Rogers or Flash Gordon would have liked them but I would rather just admire the tubes as they are. I wonder if the rings help at all with RFI--seems like they aren't spaced closely enough to shield from radio interference though.

Anyone else pull them?

 

If the phones output is not from the tubes, then this amp wouldn't even do as a phones amp for me. But, it might still be a suitable, perhaps even a welcome part of someone else's secondary system, maybe in the bedroom, coupled with some nice bookshelf speakers. But, with my audiophile mishugaz, even in the bedroom I run a 100 WPC Yamaha receiver, and PSB towers...

 

I pulled a right channel tube--no output from the right channel in the headphones, so everything in this amp is initially amplified by the two tubes on each side. It does have a tube sound, better at the speakers than in headphones, for me.

Listening yesterday and today to my "real" tube amp, KT88s P-P on each side. Definitely better bass control and overall detail, quieter too. I do like this well enough to put it in my 2nd system for awhile in place of a '90s Denon receiver. Plus it has BT built in and anybody visiting can share something from their smartphone (and control the volume and playlist) without having a tether via analog out. It is not an audiophile product but it has many virtues, along with an interesting visual design. It's one of the most fun additions to the stable in some time.

 

Mazel Tov! Enjoy, sir!

 

BTW, looked at those metal thingies around the tubes. They look more like just tube protectors, than anything else. If it's RFI/EMI filtering you're after, I would suggest a power conditioner. My old and trusted ART PS4x4 does an admirable job doing that, and cost only $100 back then. They have even cheaper models doing the same job, without the voltmeter/ampmeter indicators. It was American-made when I bought it, perhaps it still is, given the small size of the company. BTW, even Furman has some under $100 (and well above), with a good selection on Crutchfield and MusicDirect. The beauty - all your components plug into it, RFI/EMI filtering, clean straight juice, and spike protection for all pieces.

For the tubes - you can get pretty attractive dampers, the best ones being EAT (same company that makes the upmarket turntables - the higher end of Pro-Ject). They also offer good quality Czech-made tubes, if you like to roll.

EAT Cool Damper | European Audio Team »

 

Upon further investigation, it appears that some tone control circuits also utilize dual 2 channel op amps. Hmm...

 

Just picked up some M&K Bookshelf 75's and I'm even more blown away (still) by this li'l amp. Dare I say, a bit disappointed that my Yaqin MS30-L is only sounding a bit better, and that being mostly in the upper volume ranges. Currently doing some A/B comparisons.

 

Been doing some reading from John Broskie's Guide to Tube Circuit Analysis & Design on what he refers to as a Super Triode circuit involving MOSFET's and am wondering if that is what we have on our hands here in the Nobsound/Monoprice amp. That guy's got some good humor going on as well. Definitely worth the read.
(towards the bottom of the page)
Single-Ended Amplifiers & Super-Triodes »

Would sure love to see some schematics... anyone...?

 

I've been really tempted. Boy, getting the fasteners back on that xformer was fun. That glue/locking compound/anti-tamper stuff they used was a real PITA.

 

Welp, Buck Rogers ray gun cooling fin removal challenge accepted!
Google+ »

 

I think any similarities between this amp and Broskie's musings would be purely coincidental. The output stage isn't single ended anyway.

jeff

 

That's precisely why I'd love to actually see a schematic.

 

Maybe it helped reduce some of the shimmery highs?
Google+ »

 

I've been trying to post an actual photo all morning. How did you do that? Senior member privileges? I snapped quite a few throughout the whole process.